The present invention relates to a micromechanical component having a substrate made from a substrate material having a first doping, a micromechanical functional structure provided in the substrate and a cover layer to at least partially cover the micromechanical functional structure. The present invention also relates to a method for manufacturing a micromechanical component.
Micromechanical function is understood to include active function, e.g., a sensor function, or passive function, e.g., a printed conductor function.
Although it may be applied to any micromechanical component and structure, such as, for example, sensors and actuators, an exemplary embodiment according to the present invention and the underlying problem are elucidated with reference to a micromechanical component, e.g., an acceleration sensor, which may be manufactured, for example, using a silicon surface micromachining technology.
Monolithically integrated inertial sensors produced by surface micromachining technology, in which the sensitive movable structures are situated on the chip without protection (analog devices), may result in increased expenses for handling and packaging.
This problem may be circumvented by a sensor having an evaluation circuit on a separate chip, e.g., covering the structures produced by surface micromachining with a second cap wafer. This type of packaging may constitute a large share of the cost of manufacturing an acceleration sensor by surface micromachining. These costs may arise, for example, as a result of the high surface area required between the cap wafer and the sensor wafer and due to structuring (2-3 masks, bulk micromechanics) of the cap wafer.
The structure of a functional layer system and a method for the hermetic capping of sensors using surface micromachining is referred to in German Published Patent Application No. 195 37 814, in which the production of a sensor structure is explained. The cited hermetic capping is performed using a separate cap wafer of silicon, which may be structured using expensive structuring processes, such as KOH etching. The cap wafer is applied to the substrate with the sensor (sensor wafer) using a seal glass. This requires a wide bonding frame around each sensor chip to ensure an adequate adhesion and seal integrity of the cap. This may limit the number of sensor chips per sensor wafer. Due to the large amount of space required and the expensive production of the cap wafer, sensor capping may incur considerable costs.
FIG. 10 is a schematic cross-sectional view of a micromechanical component.
As shown in FIG. 10, a semiconductor substrate is identified as 10, a sacrificial layer as SL, a functional level having a micromechanical functional structure (e.g., an acceleration sensor) as FS, a seal glass as SG, a cavity as CA and a cap wafer as CW. As described above, the corresponding manufacturing process may be expensive since it requires two wafers, for example, a substrate wafer 10 and a cap wafer CW, which may be adjusted to each other.
The production of a cavity under a porous silicon layer is referred to in G. Lammel, P. Renaud, xe2x80x9cFree-standing mobile 3D microstructures of porous silicon,xe2x80x9d Proceedings of the 13th European Conference on Solid-State Transducers, Eurosensors XIII, The Hague, 1999, pages 535-536.
It is believed that an exemplary micromechanical component and manufacturing method according to the present invention allow a simple and cost-effective manufacturing of a micromechanical component, e.g., an acceleration sensor, a micropump, a flow channel, a check valve, a flow regulator, etc., using porous substrate material.
The use of such porous substrate material, e.g., porous silicon, may permit simple production of a cavity having a superimposed diaphragm in one process step. The micromechanical structures may be produced in the same process step. Thus, it is believed that advantages of an exemplary micromechanical component according to the present invention and an exemplary method for manufacturing the same include:
the production of micromechanical structures in a cavity having a superimposed diaphragm in one process step;
the exclusion of the cap wafer with wafer-to-wafer adjustment;
the inclusion of a vacuum in the cavity; and
the production of structures having complex depth profiles.
An exemplary embodiment according to the present invention is based on the micromechanical functional structure having zones made from the substrate material having a second doping, the zones being at least partially surrounded by a cavity, and the cover layer having a porous layer made from the substrate material. During manufacturing, the p-doped zones may be readily etched, when the substrate is anodized. However, the n-doped zones may not be etched or only their surfaces may be insignificantly etched.
According to an exemplary embodiment of the present invention, a sealing layer seals the pores of the porous layer. In this manner, a predetermined atmosphere under the diaphragm may be set.
According to another exemplary embodiment of the present invention, the sealing layer has an oxide layer formed on the porous zone.
According to still another exemplary embodiment of the present invention, at least one of the zones made from the substrate material having the second doping type has a supporting zone to support the porous zone.
According to yet another exemplary embodiment of the present invention, at least one of the zones made from the substrate material having the second doping type is completely detached from its surroundings.
According to still another exemplary embodiment of the present invention, the cavity includes a flow channel, which may be connected by at least two back openings.
According to yet another exemplary embodiment of the present invention, the back openings are each connected by one transfer opening, which is formed in the zone.
According to still another exemplary embodiment of the present invention, a sealing layer seals the pores of the porous layer and a detection device situated on the sealing layer piezoresistively detects the flow rate.
According to yet another exemplary embodiment of the present invention, a check valve device is provided above a corresponding transfer opening within the flow channel, the check valve device having at least one of the zones made from the substrate material having the second doping type, which is detached from its surroundings or is resiliently connected to the substrate material.
According to still another exemplary embodiment of the present invention, two check valve devices of different dimensions are provided above a corresponding transfer opening, a sealing layer sealing the pores of the porous layer and the porous zone, the sealing layer being operable as a pump diaphragm.
According to yet another exemplary embodiment of the present invention, the cavity includes a circular inner flow channel and a concentric outer flow channel, which are connected by radial ports in a separation zone made from the substrate material having the second doping type, the inner flow channel being interrupted by a bar and a back inlet opening being provided on one side of the bar and a first back outlet opening being provided on the other side of the bar and a second back outlet opening being provided in the outer flow channel, so that a medium, flowing through the back inlet opening, may be separated, specific to mass, by centrifugal force, through the first and second back outlet opening.
According to still another exemplary embodiment of the present invention, the substrate has at least one trench, which is partially filled with a doping material of the second doping type and partially filled with a filler.
According to yet another exemplary embodiment of the present invention, the substrate material is silicon.
According to still another exemplary embodiment of the present invention, the zones made from the substrate material having the second doping type are provided in the substrate at different depths.